The present disclosure generally relates to scleral eye tracking, and specifically, to scleral coil eye tracking on head mounted displays.
Scleral search coil (SSC) tracking is one technique for performing eye tracking that is both fast and accurate. One example SSC tracking system can perform eye tracking with a resolution of 0.002 degree with a relatively high sampling frequency (e.g., 8 kHz), where an optical tracking system can perform eye tracking at a lower sampling frequency (e.g., 300 Hz). Large generator coils create a uniform magnetic field across a subject's head. The subject wears, e.g., contact lenses including scleral coils. For a given eye, of the subject, depending on an orientation of the eye, the field induces a signal (e.g., a voltage or current) in the scleral coil. By examining the magnitude of the signal in the scleral coil, it is possible to estimate the orientation of the eye. But conventional SSC tracking systems are not ideal for eye tracking in systems like, e.g., head-mounted displays in virtual reality and/or augmented reality systems, where small form factor and freedom of movement are desired. In conventional SSC tracking systems, the accuracy of the estimation of the orientation of the eye scales with a size of the generator coils. For example, to obtain an accurate estimation of the orientation of the user eye, the generator coils (e.g., several meters in diameter) entirely surround the subject, and thus are inefficient for space limited systems. Moreover, the subject's head is maintained in a fixed position for estimating the orientation of the eye, thereby restricting the user's head movement.